Multi-strand cables are characterized by their characteristic impedance and crosstalk control. This characteristic impedance and crosstalk are principally determined according to the geometry of the cable, as well as according to the materials utilized to form this cable. Geometry is meant to refer to, more particularly, the disposition of cable strands inside an insulant of this cable, as well as the respective distances between each of the cable strands, and the respective distances between each cable strand and a cable braid. In fact, the cables generally comprise a braid surrounding the insulant on an exterior periphery, the insulant retaining the strands. Furthermore, the strands of the cable are twisted inside the insulant. It is known that fitting a cable in a connector has the consequence of modifying the characteristic impedance of the link at the level of this connector. This is especially due to the fact that the geometry is modified inside the connector.
As the characteristic impedance of the link is not constant, a loss in adaptation of the link is observed. Especially when high-frequency currents are transported by this link, on observes losses in the signal due to variations in the characteristic impedance and crosstalk. This is explained by the fact, among others, that the geometry of the connector is different from that of the link.
A multi-point connector ensuring continuity in the characteristic impedance and crosstalk control of a multi-strand cable is known from document FR 2 814 598. The multi-point connector of the prior art is equipped with an insulant comprising four channels in which the strands of the quadraxial cable extend when they are untwisted. The channels are arranged parallel to the longitudinal axis of said insulant in order to conserve a symmetrical quadraxial structure. Risks of crosstalk, linked to the fact that the cable strands are untwisted inside the connector, are eliminated.
FIG. 1 represents the connector for a quadraxial cable from the prior art. The multi-point connector 1 of the prior art is equipped with a cylindrical tubular body 2 in which is fitted an insulant 3 and four contacts 4 (two visible in FIG. 1). A quadraxial cable 5 is introduced at a rear extremity 6 of the body 2 so that the strands 7 of the cable 5 are introduced in the insulant 3. Each strand 7 may be connected to an end 8 of a contact 4. For this, the insulant comprises four channels. The untwisted strands 7 of the cable 5 and the ends 8 of the contacts 4 extend inside the channels, the connection between the strands 7 and the ends 8 of the contacts 4 takes place in said channels. The geometry of the disposition of channels between them, for example, the spacing of the channels between them, is calculated in such a way that the characteristic impedance of cable 5 at the level of this insulant 3 is almost identical to the characteristic impedance of cable 5.
The body 2 of the multi-point connector 1 is conductive in order to ensure a continuity of the shield with a braid 9 of the cable 5. At the location of the rear extremity of the multi-point connector 1, the cable 5 is partially stripped, that is, the cable lacks the insulating sheath 10, the braid 9 is maintained between the wall of the body 2 and a ferrule 11. The twisted strands 7 of the cable 5 extend inside the ferrule 11. The strands 7 are untwisted only at the location of the insulant 3 in order to be connected to the corresponding ends 8.
The multi-point connector of the prior art therefore allows a quadraxial structure with practically no crosstalk to be maintained inside the connector, as is the case along the entire quadraxial cable. Quadraxial structure refers to a structure in which four cable strands are disposed symmetrically with relation to each other in such a way that no crosstalk exists.
However, the quadraxial symmetry of the cable is necessarily broken at the extremities of said cable, in order to connect the cable strands to the components on an electronic board for example. To do this, it is in fact necessary to separate the two strands forming the conductors/emitters from the two strands forming the conductors/receivers to connect the strands to the corresponding components on the electronic board. Crosstalk control in a quadraxial assembly is only effective if the strands of the emitter and receiver are on the diagonals of the quadraxial square. The quadraxial structure of the cable is therefore broken at the location of the electronic board, which leads to crosstalk that may be significant, with a consequent loss of performance of the link at the location of the connection.